Conductance cell equivalent circuit

For the high-temperature oxidation of a metal we can describe the galvanic cell with an equivalent circuit incorporating the ionic and electronic contribution to the conductivity. The equivalent circuit shows the ionic resistance and the electronic resistance in series as given in Figure 15.4. Returning to oin general reaction... 

Variations of resistance with frequency can also be caused by electrode polarization. A conductance cell can be represented in a simplified way as resistance and capacitance in series, the latter being the double layer capacitance at the electrodes. Only if this capacitance is sufficiently large will the measured resistance be independent of frequency. To accomplish this, electrodes are often covered with platinum black 2>. This is generally unsuitable in nonaqueous solvent studies because of possible catalysis of chemical reactions and because of adsorption problems encountered with dilute solutions required for useful data. The equivalent circuit for a conductance cell is also complicated by impedances due to faradaic processes and the geometric capacity of the cell 2>3( . 

Here, we concentrate on cell 1 and assume negligible electrode effects. If a constant current is switched on, both a faradaic as well as a displacement current flows (cf. Section I). Hence the actual current can be ionic/electronic or capacitive, the relative proportions depending on the electronic (creon) and ionic (crion) conductivities and the dielectric constant. Correspondingly, the elements are, as long as creon and crion are summed locally, in parallel (oo denotes the bulk and / , = ReonRtJ Re(m + 70) and the equivalent circuit is given by (cf. also Eq. (5))... 

The phenomena important in electrolytic conductance have been discussed96 and are represented by the electrical equivalent circuit of a conductance cell shown in Figure 6.24a. 

Figure 6.24 (a) Electrical equivalent circuit for a conductance cell (b) AC bridge with the cell impedance balanced by a series R-C combination (c) AC bridge with the cell impedance balanced by a parallel R-C combination (see Table 6.7). 

Figure 4.33. Equivalent circuit of a catalyst layer [8]. (Reproduced by permission of the authors and of ECS—The Electrochemical Society, from Lefebvre MC, Martin RB, Pickup PG. Characterization of ionic conductivity within proton exchange membrane fuel cell gas diffusion electrodes by impedance spectroscopy.)...

Conductive polymers are not used in fuel cells. However, the equivalent circuit of conductive polymers is similar to that of catalyst layers, which may help to understand impedance spectra in fuel cells. In general, the electric circuits of... 

Figure 5.8. a Schematic diagram of a two-probe conductivity cell [9], (Reproduced by permission of ECS—The Electrochemical Society, from Xie Z, Song C, Andreaus B, Navessin T, Shi Z, Zhang J, Eloldcroft S. Discrepancies in the measurement of ionic conductivity of PEMs using two- and four-probe AC impedance spectroscopy) b Equivalent circuit of the two-probe method. 

On the other hand, the intervening media used in electrophoresis have much lower conductivity, and an equivalent circuit for an electrophoresis cell includes a resistor between the capacitors at the electrode-solution interfaces. Across the support medium, potential is now (usually) a linear function of distance, and the electric field thus generated is responsible for driving the electrophoretic separation. Electrophoresis occurs at the electrodes used in electrophoresis, to maintain the... 

Fig. 6.5 Schematic diagram of a conductivity cell (a) and its impedance representation as an equivalent circuit (b). Capacitances Ci and C2 are at the electrode I solution...

Figure 9 Equivalent circuit accounting for the electrode-polarization effect. Fq(0 is a rapidly increasing voltage step I(i) is a current Zq is the coaxial line impedance Cp is the capacitance of electrode polarization Cq is an empty cell capacitance filled with a dielectric sample of permittivity e and conductivity 1/R Vp(t) and Fg(i) are the voltages at the appropriate parts of the circuit. (From Ref. 72. With permission from Elsevier Science B.V.)...

Let us examine a flat-plate electrode at zero potential, positioned in a cell in parallel with a perfectly conductive counter electrode, as shown in Fig. 10.3.lOA. The current is fed from the top end of the resistive electrode. In this case, the electrolytic current decreases graducilly along the working surface from the top to the bottom because of the ohmic resistance within the electrode. The current density, i(x), at the distance x from the current feed, calculated by using the equivalent circuit shown in (B), is as follows [1,13] ... 

Liu, M. (1998). Equivalent circuit approximation to porous mixed-conducting oxygen electrodes in solid state cells. J Electrochem. Soc. 145 142-154. 

The function of the AC technique is the following the equivalent circuit of a conductance cell (Fig. 19) is quite complex and the conditions of experiments must be such that the solution resistance R is the principal component that determines the observed cell response. The individual parts of the equivalent circuit in Fig. 19 should be easy to understand on the basis of the description given in section 2.2. 

Conductivity is measured in a cell containing two plates as electrodes (usually made of platinum) through which the column effluent flows. The electrodes have a known surface area and are located in the cell at a fixed distance. The cell is connected in an a.c. circuit and is characterized by the double-layer capacitance Co. the cell capacitance Cc, and the electrolyte resistance f s of the sample solution (see the equivalent circuit diagram in Fig. 13). 

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